Conventional scanning electron microscopes (SEM) are configured to scan an electron beam across a portion of a sample and to detect electrons emerging from the sample upon directing the electron beam to the portion of the sample. An intensity of electrons emerging from the sample is detected by an electron detector and associated with a location to which the electron beam is currently directed. Accordingly, an intensity distribution may be determined using the scanning electron microscope, and an image representation of the portion of the sample may be generated based on the intensity distribution.
Usually, a zoom parameter may be defined by a user of the scanning electron microscope in order to select a magnification by which the portion of the sample is magnified in comparison to its actual size. In the scanning electron microscope, the directing of the electron beam depends on the zoom parameter, in particular the electron beam is deflected in dependence of the zoom parameter so that a distance between locations of incidence of the electron beam onto the sample depends on the zoom parameter. For example, a scanning resolution, i.e. a number of locations of incidence of the electron beam onto the sample per unit length or per unit area, increases with increasing zoom parameter, and likewise the scanning resolution decreases with decreasing zoom parameter.
A spatial resolution of the images obtainable using a SEM depends on the size of the spot formed by the electron beam on the sample, which in turn depends on the wavelength of the electrons of the electron beam and the electron-optical system that produces the electron beam. Furthermore, the spatial resolution is limited by an interaction volume in which the electrons of the electron beam interact with the sample. Both the size of the spot and the interaction volume are both large compared to inter-atomic distances of the atoms constituting the sample, so that the crystallographic structure of the sample cannot be resolved using conventional scanning electron microscopes.
In order to resolve the crystal structure of the sample, transmission electron microscopes (TEM) employing electron beams of electrons having kinetic energies much greater than the kinetic energies of the electrons of the electron beams used in a SEM can be used. However, as the kinetic energies of the electrons used in SEM and TEM usually differ by at least one order of magnitude, SEM and TEM are not combined into a single microscope. Accordingly, in order to determine and to visualize the crystal structure of the sample, the sample is transferred from the SEM used to obtain SEM images to a TEM used to obtain images of the crystal structure of the sample. This transferring of the sample to different microscopes implies a plurality of disadvantages such as deterioration of the sample over time, damage of the sample during the transferring of the sample between the microscopes, etc.